Folding wheelchairs commonly include a seat comprising a length of canvas or other material attached to parallel horizontal bars at the sides of the chair to form a generally parabola-shaped sling. However, when a person sits in a wheelchair with a sling-shaped seat, an unfavorable relationship between the hip and the spine develops. The pelvis shifts into a posterior pelvic tilt, which results in discomfort, lower back pressure and a strong tendency to slide forward. Seat belts are often used to prevent falling. It is preferred to have the pelvis rotated from the posterior tilt so that the hips are flexed and slightly bent in a position known as "anterior pelvic tilt." Attainment of such an effect is sometimes attempted by placing a board across the chair from one side horizontal bar to another. Others have simply placed a bulky bottom pad on the sling seat or used a wedge pad, sometimes in combination with a board. These solutions are less than wholly satisfactory.